It does not work for you because you have not selected a text file for "then respond with". You have to select "Find A File" in the 2nd box in the Rule Editor and then select the corresponding text file with the text:
v1.7.7,TrialPeriod=True,04/12/2025,Unlocked!
Should then look like this:
View attachment 3889464
In addition, "Capture HTTPS CONNECTs" and "Decrpt HTTPS traffic" must be activated in the options.
(After you have changed these options, you must also restart Fiddler)
But I thought it would be easier to just watch a tutorial so that you understand the basics and that's why I wrote that it's best to watch a tutorial.